PDCD1 and melanoma: However, Chen et al. (2018) recently proposed that exosomal PD-L1 is associated with an anti-PD-1 response in melanoma, and we are also performing further research to evaluate whether PD-L1-positive exosomes in plasma can be used as a surrogate marker of PD-L1 expression in tumor tissue to predict the efficacy of PD-1/PD-L1 immunotherapy.